The invention pertains to the field of YIG devices, and, more particularly, to the field of heater designs for YIG spheres.
YIG devices must typically operate over a very wide range of temperatures. Since certain properties of YIG spheres are temperature dependent, the practice was adopted in the prior art of using heaters to heat the rods which support the YIG spheres thereby heating the spheres. This caused the temperature of the spheres to be under the control of the designer of the YIG device and not be subject to the ambient conditions. This allowed the designer to have better control over the performance of the YIG device by reducing the effect of ambient temperature as a design factor.
FIG. 1 shows an early prior art YIG filter heater design. A heater block 10 supports a brass collet 12 of a sphere support assembly. The brass collet 12 is coupled to a beryllium-oxide rod 14 which has a YIG sphere 16 mounted at the tip thereof. Typically, the YIG sphere is 0.010 to 0.026 inches in diameter. The heater block 10 has a slot cut therein which is crimped before the brass collet is inserted so as to form a press fit between the heater block and the brass collet to provide solid contact for better heat transfer efficiency. Twin heater pellets 20 and 22 are affixed to flat surfaces 24 and 26 of the heater block so as to transfer heat to the heater block from the positive temperature coefficient barium titanate heater pellets that function as heater elements.
This design was used in the early 1980's. The drawback of this design was that the only contact between the heater block and the brass collet was at the crimped edge of the heater block. This led to a small area of contact between the heater block and the brass collet which impaired the heat transfer efficiency. Also, the heat transfer path from the heater pellets and YIG sphere was complex in that many interfaces had to be traversed. Specifically, heat from the heater pellet passes to the heater block and from there to the brass collet. From the brass collet, the heat passes to the beryllium-oxide rod and from there to the YIG sphere.
FIG. 2 shows a later prior art heater design. In this design a brass heater block 30 has holes formed therein to receive the beryllium-oxide rod 34 of each of a plurality of YIG support rods. Hole 40 is typical of these holes. The sphere rod 34 of each YIG support rod assembly rests in a corresponding trough 36 formed in a step part 38 of the heater block so as to be aligned with the hole 40. The sphere rods are clamped down to the heater block in their respective troughs by a beryllium copper spring clip 42 which is fastened to the heater block via a pair of screws 44 and 46. A rubber gasket 48 may be interposed between the spring clip and the heater block.
The design of FIG. 2 is very complicated to manufacture and does not always apply equal clamping pressure to each sphere rod assembly. This tends to result from bowing of the spring clip caused by the pressure exerted by the screws 44 and 46. This tendency is somewhat alleviated by the inclusion of the gasket 48, but results in a design which is overly complicated and difficult and expensive to manufacture.
In another prior art design by Trak Microwave, Inc., a heater block having a piano wire spring element incorporated therein was used to support the YIG support rod. The piano wire was run through the heater block in such a way that when the YIG support rod was inserted, the piano wire was deflected so as to bias the YIG support rod against the wall of the guide hole.
Therefore a need has arisen for a simple, easy to manufacture heater design which applies equal pressure to all sphere rod assemblies to clamp all rods to the heater block and insure equal heating of each sphere.